Love her or loathe her, Margaret Thatcher changed the industrial landscape of Britain. It is 10 years to the day since she was ousted in a palace coup. But the main legacy of her time in Downing Street lives on, not just in Britain but across the world.

The shorthand version of the Thatcher years, as retold in the Iron Lady's memoirs, and on the after-dinner circuit - where she earns an estimated £1.5m a year - is that Britain was changed from the land of Red Robbo and wildcat strikes to the land of "Sid" and the share-owning democracy. In one stroke, the dead hand of the state was removed from the economy, unleashing a new spirit of enterprise and derring do.

But memoirs, like memory, can play tricks. By the time the usually steely-eyed Lady Thatcher made her tearful departure in November 1990, one in four of the population owned shares and more than 40 former state-owned businesses had been privatised, a process which affected more than 600,000 workers in former nationalised industries.

Privatisation was, however, no overnight revolution; rather it was a slow-burn process that only really began in Mrs Thatcher's second term. In fact Jim Callahan sold a chunk of BP in the 1970s to to keep the International Monetary Fund happy. What is more, the record of some companies that were denationalised looks different today from the late 80s, when tycoons like Lord King at British Airways were members of the prime minister's inner court.

Mad dash for shares

The truth is that privatisation hardly featured at all between 1979 and 1983, when Mrs Thatcher was preoccupied by three struggles - the fight against inflation, the fight against the unions and the fight against the Argentines. Even during the second term, from 1983 to 1987 - easily the most radical of the four successive Conservative terms in office - there was no real conception of how a scheme to make money for the Treasury could be used as a weapon to win votes.

It was only after the mad dash for shares in British Telecom in 1984 that the penny dropped in Downing Street. Privatisation was not just about ownership and industrial organisation, it was also about politics. As such, the BT sell off was followed by the privatisation of British Gas in 1986 and of Rolls-Royce, British Airways and the British Airports Authority in 1987.

Apart from the unions and the Labour party, everybody seemed happy. The government had extra cash to spend on tax cuts, voters had shares which were going up in value and those running the companies had freedom to act and much fat ter pay packets. But how much has really changed? To be sure, many of those working in the old nationalised industries have lost their jobs as the newly cost-conscious companies responded to shareholder demands to boost productivity and profits. But BT is still seen as flabby and staid, BA is struggling to compete in the global airlines business, and Railtrack - a company sold off long after Mrs Thatcher was ousted - is dogged by controversy about whether privatisation is to blame for the state of the nation's railways. The tough regulation to prevent the privatised utilities exploiting their natural monopolies has made some of them hanker after giving up their PLC status.

In her memoirs, the former prime minister evocatively described the sale of state assets as essential to "eroding the corro sive and corrupting effects of socialism". Yet five years after she left office, a star was created out of a 30-stone pink and black pig named Cedric, who was to come to symbolise corporate excess with its snout buried in the "trough of privatisation". Ironically, though, the level of pay being protested about then - a 75% rise for chief executive Cedric Brown, to £475,000 and potential performance-related bonus of £594,000 - would now barely cause even a raised eyebrow.

Unsurprisingly, Lady Thatcher and her teams of politicial and financial advisers prefer not to dwell on the boardroom self-enrichment that followed privatisation, arguing instead that there were beneficial effects for the wider economy.

Tony Carlisle, a City public relations adviser involved in 90% of the privatisations, acknowledges: "One of the key accusations of privatisations is that it works for the bosses and the shareholders, but ... pity about the poor consumer."

But he argues that privatisation actually served the consumer well. Through deregulation and increased competition, there is more choice about which company gas, electricity and telephone services can be bought.

Without privatisation, companies such as Vodafone and Energis might never have been created. A senior corporate finance executive closely involved in the privatisation says: "You may argue about the pricing, the public policy and the structure of the deals but if it had not been done you would not have the competition we now see across all industries".

The more cynical take the view that privatisation demonstrated that being British was not best. One highly regarded City analyst says: "In general, companies with British in their names haven't done very well. Being British quickly became too parochial."

Words such as "globalisation" have quickly eclipsed "privatisation" in the City's lexicon of catchphrases. The big, national monopolies that were privatised increasingly drew their customers outside national boundaries.

"British" is now eradicated from British Steel, after merging with Hoogovens of Holland to form Corus; from British Gas, now three separate companies, only one of which refers to itself as BG. British Petroleum has long been BP and now BP Amoco after its multi-billion dollar takeover of the US company.

Another frequent criticism is that the companies were sold off too cheaply. Another City analyst warns this can be a too simple conclusion drawn from the way in which many of the share sales were overscribed. Not all the share sales were successful. BP, for instance, hit the market in the midst of a stock market crash, leaving many banks licking their wounds.

Tell Sid

Yet, an analysis of the companies which were privatised during the Thatcher years shows that the privatisation portfolio, constructed for the Guardian by investment bank ING Barings, outperformed the benchmark FTSE 100 for most of the period. An indication that investors were sold the companies too cheaply, or a reflection of sound management which outpaced the rest of the industry?

To one City analyst it is almost irrelevant whether the privatisation portfolio outperformed the market. "The 'Tell Sid' campaign sticks in people's minds. It made people more aware that the equity market could be a form of saving for the future just as it became the state could no longer provide for old age," the analyst said.

Tony Alt, a corporate financier at investment Rothschild who was involved in many of the major privatisations, regards the most important legacy as creating "a platform for privatisations around the globe".

More than £400bn of assets have now been privatised in countries as diverse as the Czech republic and New Zealand, and a word which gained currency during Lady Thatcher's government is now internationally recognised.

But the real political impact of privatisation has not been in Prague or Wellington but in London. In 1983 when he first became an MP, Tony Blair fought on a Labour manifesto committed to an extension of state ownership. The strength of Mrs Thatcher's enduring legacy is that Labour has not only turned its back on nationalisation, but now has privatisation plans of its own.